2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 Marco Costalba
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
38 #include "ucioption.h"
47 int Position::castleRightsMask[64];
49 Key Position::zobrist[2][8][64];
50 Key Position::zobEp[64];
51 Key Position::zobCastle[16];
52 Key Position::zobMaterial[2][8][16];
53 Key Position::zobSideToMove;
54 Key Position::zobExclusion;
56 Score Position::PieceSquareTable[16][64];
58 static bool RequestPending = false;
63 CheckInfo::CheckInfo(const Position& pos) {
65 Color us = pos.side_to_move();
66 Color them = opposite_color(us);
68 ksq = pos.king_square(them);
69 dcCandidates = pos.discovered_check_candidates(us);
71 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
72 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
73 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
74 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
75 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
76 checkSq[KING] = EmptyBoardBB;
79 Position::Position(const Position& pos) {
83 Position::Position(const string& fen) {
88 /// Position::from_fen() initializes the position object with the given FEN
89 /// string. This function is not very robust - make sure that input FENs are
90 /// correct (this is assumed to be the responsibility of the GUI).
92 void Position::from_fen(const string& fen) {
94 static const string pieceLetters = "KQRBNPkqrbnp";
95 static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
103 for ( ; fen[i] != ' '; i++)
107 // Skip the given number of files
108 file += (fen[i] - '1' + 1);
111 else if (fen[i] == '/')
117 size_t idx = pieceLetters.find(fen[i]);
118 if (idx == string::npos)
120 std::cout << "Error in FEN at character " << i << std::endl;
123 Square square = make_square(file, rank);
124 put_piece(pieces[idx], square);
130 if (fen[i] != 'w' && fen[i] != 'b')
132 std::cout << "Error in FEN at character " << i << std::endl;
135 sideToMove = (fen[i] == 'w' ? WHITE : BLACK);
141 std::cout << "Error in FEN at character " << i << std::endl;
146 while(strchr("KQkqabcdefghABCDEFGH-", fen[i])) {
152 else if(fen[i] == 'K') allow_oo(WHITE);
153 else if(fen[i] == 'Q') allow_ooo(WHITE);
154 else if(fen[i] == 'k') allow_oo(BLACK);
155 else if(fen[i] == 'q') allow_ooo(BLACK);
156 else if(fen[i] >= 'A' && fen[i] <= 'H') {
157 File rookFile, kingFile = FILE_NONE;
158 for(Square square = SQ_B1; square <= SQ_G1; square++)
159 if(piece_on(square) == WK)
160 kingFile = square_file(square);
161 if(kingFile == FILE_NONE) {
162 std::cout << "Error in FEN at character " << i << std::endl;
165 initialKFile = kingFile;
166 rookFile = File(fen[i] - 'A') + FILE_A;
167 if(rookFile < initialKFile) {
169 initialQRFile = rookFile;
173 initialKRFile = rookFile;
176 else if(fen[i] >= 'a' && fen[i] <= 'h') {
177 File rookFile, kingFile = FILE_NONE;
178 for(Square square = SQ_B8; square <= SQ_G8; square++)
179 if(piece_on(square) == BK)
180 kingFile = square_file(square);
181 if(kingFile == FILE_NONE) {
182 std::cout << "Error in FEN at character " << i << std::endl;
185 initialKFile = kingFile;
186 rookFile = File(fen[i] - 'a') + FILE_A;
187 if(rookFile < initialKFile) {
189 initialQRFile = rookFile;
193 initialKRFile = rookFile;
197 std::cout << "Error in FEN at character " << i << std::endl;
204 while (fen[i] == ' ')
208 if ( i <= fen.length() - 2
209 && (fen[i] >= 'a' && fen[i] <= 'h')
210 && (fen[i+1] == '3' || fen[i+1] == '6'))
211 st->epSquare = square_from_string(fen.substr(i, 2));
213 // Various initialisation
214 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
215 castleRightsMask[sq] = ALL_CASTLES;
217 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
218 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
219 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
220 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
221 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
222 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
226 st->key = compute_key();
227 st->pawnKey = compute_pawn_key();
228 st->materialKey = compute_material_key();
229 st->value = compute_value();
230 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
231 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
235 /// Position::to_fen() converts the position object to a FEN string. This is
236 /// probably only useful for debugging.
238 const string Position::to_fen() const {
240 static const string pieceLetters = " PNBRQK pnbrqk";
244 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
247 for (File file = FILE_A; file <= FILE_H; file++)
249 Square sq = make_square(file, rank);
250 if (!square_is_occupied(sq))
256 fen += (char)skip + '0';
259 fen += pieceLetters[piece_on(sq)];
262 fen += (char)skip + '0';
264 fen += (rank > RANK_1 ? '/' : ' ');
266 fen += (sideToMove == WHITE ? "w " : "b ");
267 if (st->castleRights != NO_CASTLES)
269 if (can_castle_kingside(WHITE)) fen += 'K';
270 if (can_castle_queenside(WHITE)) fen += 'Q';
271 if (can_castle_kingside(BLACK)) fen += 'k';
272 if (can_castle_queenside(BLACK)) fen += 'q';
277 if (ep_square() != SQ_NONE)
278 fen += square_to_string(ep_square());
286 /// Position::print() prints an ASCII representation of the position to
287 /// the standard output. If a move is given then also the san is print.
289 void Position::print(Move m) const {
291 static const string pieceLetters = " PNBRQK PNBRQK .";
293 // Check for reentrancy, as example when called from inside
294 // MovePicker that is used also here in move_to_san()
298 RequestPending = true;
300 std::cout << std::endl;
303 string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
304 std::cout << "Move is: " << col << move_to_san(*this, m) << std::endl;
306 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
308 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
309 for (File file = FILE_A; file <= FILE_H; file++)
311 Square sq = make_square(file, rank);
312 Piece piece = piece_on(sq);
313 if (piece == EMPTY && square_color(sq) == WHITE)
316 char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
317 std::cout << '|' << col << pieceLetters[piece] << col;
319 std::cout << '|' << std::endl;
321 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
322 << "Fen is: " << to_fen() << std::endl
323 << "Key is: " << st->key << std::endl;
325 RequestPending = false;
329 /// Position::copy() creates a copy of the input position.
331 void Position::copy(const Position& pos) {
333 memcpy(this, &pos, sizeof(Position));
334 saveState(); // detach and copy state info
338 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
339 /// king) pieces for the given color and for the given pinner type. Or, when
340 /// template parameter FindPinned is false, the pieces of the given color
341 /// candidate for a discovery check against the enemy king.
342 /// Note that checkersBB bitboard must be already updated.
344 template<bool FindPinned>
345 Bitboard Position::hidden_checkers(Color c) const {
347 Bitboard result = EmptyBoardBB;
348 Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
350 // Pinned pieces protect our king, dicovery checks attack
352 Square ksq = king_square(FindPinned ? c : opposite_color(c));
354 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
355 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
357 if (FindPinned && pinners)
358 pinners &= ~st->checkersBB;
362 Square s = pop_1st_bit(&pinners);
363 Bitboard b = squares_between(s, ksq) & occupied_squares();
367 if ( !(b & (b - 1)) // Only one bit set?
368 && (b & pieces_of_color(c))) // Is an our piece?
375 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
376 /// king) pieces for the given color.
378 Bitboard Position::pinned_pieces(Color c) const {
380 return hidden_checkers<true>(c);
384 /// Position:discovered_check_candidates() returns a bitboard containing all
385 /// pieces for the given side which are candidates for giving a discovered
388 Bitboard Position::discovered_check_candidates(Color c) const {
390 return hidden_checkers<false>(c);
393 /// Position::attackers_to() computes a bitboard containing all pieces which
394 /// attacks a given square.
396 Bitboard Position::attackers_to(Square s) const {
398 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
399 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
400 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
401 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
402 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
403 | (attacks_from<KING>(s) & pieces(KING));
406 /// Position::attacks_from() computes a bitboard of all attacks
407 /// of a given piece put in a given square.
409 Bitboard Position::attacks_from(Piece p, Square s) const {
411 assert(square_is_ok(s));
415 case WP: return attacks_from<PAWN>(s, WHITE);
416 case BP: return attacks_from<PAWN>(s, BLACK);
417 case WN: case BN: return attacks_from<KNIGHT>(s);
418 case WB: case BB: return attacks_from<BISHOP>(s);
419 case WR: case BR: return attacks_from<ROOK>(s);
420 case WQ: case BQ: return attacks_from<QUEEN>(s);
421 case WK: case BK: return attacks_from<KING>(s);
428 /// Position::move_attacks_square() tests whether a move from the current
429 /// position attacks a given square.
431 bool Position::move_attacks_square(Move m, Square s) const {
433 assert(move_is_ok(m));
434 assert(square_is_ok(s));
436 Square f = move_from(m), t = move_to(m);
438 assert(square_is_occupied(f));
440 if (bit_is_set(attacks_from(piece_on(f), t), s))
443 // Move the piece and scan for X-ray attacks behind it
444 Bitboard occ = occupied_squares();
445 Color us = color_of_piece_on(f);
448 Bitboard xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
449 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN))) & pieces_of_color(us);
451 // If we have attacks we need to verify that are caused by our move
452 // and are not already existent ones.
453 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
457 /// Position::find_checkers() computes the checkersBB bitboard, which
458 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
459 /// currently works by calling Position::attackers_to, which is probably
460 /// inefficient. Consider rewriting this function to use the last move
461 /// played, like in non-bitboard versions of Glaurung.
463 void Position::find_checkers() {
465 Color us = side_to_move();
466 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
470 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
472 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
475 assert(move_is_ok(m));
476 assert(pinned == pinned_pieces(side_to_move()));
478 // Castling moves are checked for legality during move generation.
479 if (move_is_castle(m))
482 Color us = side_to_move();
483 Square from = move_from(m);
485 assert(color_of_piece_on(from) == us);
486 assert(piece_on(king_square(us)) == piece_of_color_and_type(us, KING));
488 // En passant captures are a tricky special case. Because they are
489 // rather uncommon, we do it simply by testing whether the king is attacked
490 // after the move is made
493 Color them = opposite_color(us);
494 Square to = move_to(m);
495 Square capsq = make_square(square_file(to), square_rank(from));
496 Bitboard b = occupied_squares();
497 Square ksq = king_square(us);
499 assert(to == ep_square());
500 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
501 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
502 assert(piece_on(to) == EMPTY);
505 clear_bit(&b, capsq);
508 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
509 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
512 // If the moving piece is a king, check whether the destination
513 // square is attacked by the opponent.
514 if (type_of_piece_on(from) == KING)
515 return !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
517 // A non-king move is legal if and only if it is not pinned or it
518 // is moving along the ray towards or away from the king.
520 || !bit_is_set(pinned, from)
521 || (direction_between_squares(from, king_square(us)) == direction_between_squares(move_to(m), king_square(us))));
525 /// Position::pl_move_is_evasion() tests whether a pseudo-legal move is a legal evasion
527 bool Position::pl_move_is_evasion(Move m, Bitboard pinned) const
531 Color us = side_to_move();
532 Square from = move_from(m);
533 Square to = move_to(m);
535 // King moves and en-passant captures are verified in pl_move_is_legal()
536 if (type_of_piece_on(from) == KING || move_is_ep(m))
537 return pl_move_is_legal(m, pinned);
539 Bitboard target = checkers();
540 Square checksq = pop_1st_bit(&target);
542 if (target) // double check ?
545 // Our move must be a blocking evasion or a capture of the checking piece
546 target = squares_between(checksq, king_square(us)) | checkers();
547 return bit_is_set(target, to) && pl_move_is_legal(m, pinned);
551 /// Position::move_is_check() tests whether a pseudo-legal move is a check
553 bool Position::move_is_check(Move m) const {
555 return move_is_check(m, CheckInfo(*this));
558 bool Position::move_is_check(Move m, const CheckInfo& ci) const {
561 assert(move_is_ok(m));
562 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
563 assert(color_of_piece_on(move_from(m)) == side_to_move());
564 assert(piece_on(ci.ksq) == piece_of_color_and_type(opposite_color(side_to_move()), KING));
566 Square from = move_from(m);
567 Square to = move_to(m);
568 PieceType pt = type_of_piece_on(from);
571 if (bit_is_set(ci.checkSq[pt], to))
575 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
577 // For pawn and king moves we need to verify also direction
578 if ( (pt != PAWN && pt != KING)
579 ||(direction_between_squares(from, ci.ksq) != direction_between_squares(to, ci.ksq)))
583 // Can we skip the ugly special cases ?
584 if (!move_is_special(m))
587 Color us = side_to_move();
588 Bitboard b = occupied_squares();
590 // Promotion with check ?
591 if (move_is_promotion(m))
595 switch (move_promotion_piece(m))
598 return bit_is_set(attacks_from<KNIGHT>(to), ci.ksq);
600 return bit_is_set(bishop_attacks_bb(to, b), ci.ksq);
602 return bit_is_set(rook_attacks_bb(to, b), ci.ksq);
604 return bit_is_set(queen_attacks_bb(to, b), ci.ksq);
610 // En passant capture with check? We have already handled the case
611 // of direct checks and ordinary discovered check, the only case we
612 // need to handle is the unusual case of a discovered check through the
616 Square capsq = make_square(square_file(to), square_rank(from));
618 clear_bit(&b, capsq);
620 return (rook_attacks_bb(ci.ksq, b) & pieces(ROOK, QUEEN, us))
621 ||(bishop_attacks_bb(ci.ksq, b) & pieces(BISHOP, QUEEN, us));
624 // Castling with check ?
625 if (move_is_castle(m))
627 Square kfrom, kto, rfrom, rto;
633 kto = relative_square(us, SQ_G1);
634 rto = relative_square(us, SQ_F1);
636 kto = relative_square(us, SQ_C1);
637 rto = relative_square(us, SQ_D1);
639 clear_bit(&b, kfrom);
640 clear_bit(&b, rfrom);
643 return bit_is_set(rook_attacks_bb(rto, b), ci.ksq);
650 /// Position::do_move() makes a move, and saves all information necessary
651 /// to a StateInfo object. The move is assumed to be legal.
652 /// Pseudo-legal moves should be filtered out before this function is called.
654 void Position::do_move(Move m, StateInfo& newSt) {
657 do_move(m, newSt, ci, move_is_check(m, ci));
660 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
663 assert(move_is_ok(m));
665 Bitboard key = st->key;
667 // Copy some fields of old state to our new StateInfo object except the
668 // ones which are recalculated from scratch anyway, then switch our state
669 // pointer to point to the new, ready to be updated, state.
670 struct ReducedStateInfo {
671 Key pawnKey, materialKey;
672 int castleRights, rule50, pliesFromNull;
678 memcpy(&newSt, st, sizeof(ReducedStateInfo));
682 // Save the current key to the history[] array, in order to be able to
683 // detect repetition draws.
684 history[gamePly] = key;
687 // Update side to move
688 key ^= zobSideToMove;
690 // Increment the 50 moves rule draw counter. Resetting it to zero in the
691 // case of non-reversible moves is taken care of later.
695 if (move_is_castle(m))
702 Color us = side_to_move();
703 Color them = opposite_color(us);
704 Square from = move_from(m);
705 Square to = move_to(m);
706 bool ep = move_is_ep(m);
707 bool pm = move_is_promotion(m);
709 Piece piece = piece_on(from);
710 PieceType pt = type_of_piece(piece);
711 PieceType capture = ep ? PAWN : type_of_piece_on(to);
713 assert(color_of_piece_on(from) == us);
714 assert(color_of_piece_on(to) == them || square_is_empty(to));
715 assert(!(ep || pm) || piece == piece_of_color_and_type(us, PAWN));
716 assert(!pm || relative_rank(us, to) == RANK_8);
719 do_capture_move(key, capture, them, to, ep);
722 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
724 // Reset en passant square
725 if (st->epSquare != SQ_NONE)
727 key ^= zobEp[st->epSquare];
728 st->epSquare = SQ_NONE;
731 // Update castle rights, try to shortcut a common case
732 int cm = castleRightsMask[from] & castleRightsMask[to];
733 if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
735 key ^= zobCastle[st->castleRights];
736 st->castleRights &= castleRightsMask[from];
737 st->castleRights &= castleRightsMask[to];
738 key ^= zobCastle[st->castleRights];
741 // Prefetch TT access as soon as we know key is updated
745 Bitboard move_bb = make_move_bb(from, to);
746 do_move_bb(&(byColorBB[us]), move_bb);
747 do_move_bb(&(byTypeBB[pt]), move_bb);
748 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
750 board[to] = board[from];
753 // Update piece lists, note that index[from] is not updated and
754 // becomes stale. This works as long as index[] is accessed just
755 // by known occupied squares.
756 index[to] = index[from];
757 pieceList[us][pt][index[to]] = to;
759 // If the moving piece was a pawn do some special extra work
762 // Reset rule 50 draw counter
765 // Update pawn hash key
766 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
768 // Set en passant square, only if moved pawn can be captured
769 if ((to ^ from) == 16)
771 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
773 st->epSquare = Square((int(from) + int(to)) / 2);
774 key ^= zobEp[st->epSquare];
779 // Update incremental scores
780 st->value += pst_delta(piece, from, to);
783 st->capture = capture;
785 if (pm) // promotion ?
787 PieceType promotion = move_promotion_piece(m);
789 assert(promotion >= KNIGHT && promotion <= QUEEN);
791 // Insert promoted piece instead of pawn
792 clear_bit(&(byTypeBB[PAWN]), to);
793 set_bit(&(byTypeBB[promotion]), to);
794 board[to] = piece_of_color_and_type(us, promotion);
796 // Update material key
797 st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
798 st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
800 // Update piece counts
801 pieceCount[us][PAWN]--;
802 pieceCount[us][promotion]++;
804 // Update piece lists, move the last pawn at index[to] position
805 // and shrink the list. Add a new promotion piece to the list.
806 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
807 index[lastPawnSquare] = index[to];
808 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
809 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
810 index[to] = pieceCount[us][promotion] - 1;
811 pieceList[us][promotion][index[to]] = to;
813 // Partially revert hash keys update
814 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
815 st->pawnKey ^= zobrist[us][PAWN][to];
817 // Partially revert and update incremental scores
818 st->value -= pst(us, PAWN, to);
819 st->value += pst(us, promotion, to);
822 st->npMaterial[us] += piece_value_midgame(promotion);
825 // Update the key with the final value
828 // Update checkers bitboard, piece must be already moved
829 st->checkersBB = EmptyBoardBB;
834 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
838 if (bit_is_set(ci.checkSq[pt], to))
839 st->checkersBB = SetMaskBB[to];
842 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
845 st->checkersBB |= (attacks_from<ROOK>(ci.ksq) & pieces(ROOK, QUEEN, us));
848 st->checkersBB |= (attacks_from<BISHOP>(ci.ksq) & pieces(BISHOP, QUEEN, us));
854 sideToMove = opposite_color(sideToMove);
855 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
861 /// Position::do_capture_move() is a private method used to update captured
862 /// piece info. It is called from the main Position::do_move function.
864 void Position::do_capture_move(Bitboard& key, PieceType capture, Color them, Square to, bool ep) {
866 assert(capture != KING);
870 if (ep) // en passant ?
872 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
874 assert(to == st->epSquare);
875 assert(relative_rank(opposite_color(them), to) == RANK_6);
876 assert(piece_on(to) == EMPTY);
877 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
879 board[capsq] = EMPTY;
882 // Remove captured piece
883 clear_bit(&(byColorBB[them]), capsq);
884 clear_bit(&(byTypeBB[capture]), capsq);
885 clear_bit(&(byTypeBB[0]), capsq);
888 key ^= zobrist[them][capture][capsq];
890 // Update incremental scores
891 st->value -= pst(them, capture, capsq);
893 // If the captured piece was a pawn, update pawn hash key,
894 // otherwise update non-pawn material.
896 st->pawnKey ^= zobrist[them][PAWN][capsq];
898 st->npMaterial[them] -= piece_value_midgame(capture);
900 // Update material hash key
901 st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
903 // Update piece count
904 pieceCount[them][capture]--;
906 // Update piece list, move the last piece at index[capsq] position
908 // WARNING: This is a not perfectly revresible operation. When we
909 // will reinsert the captured piece in undo_move() we will put it
910 // at the end of the list and not in its original place, it means
911 // index[] and pieceList[] are not guaranteed to be invariant to a
912 // do_move() + undo_move() sequence.
913 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
914 index[lastPieceSquare] = index[capsq];
915 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
916 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
918 // Reset rule 50 counter
923 /// Position::do_castle_move() is a private method used to make a castling
924 /// move. It is called from the main Position::do_move function. Note that
925 /// castling moves are encoded as "king captures friendly rook" moves, for
926 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
928 void Position::do_castle_move(Move m) {
930 assert(move_is_ok(m));
931 assert(move_is_castle(m));
933 Color us = side_to_move();
934 Color them = opposite_color(us);
936 // Reset capture field
937 st->capture = NO_PIECE_TYPE;
939 // Find source squares for king and rook
940 Square kfrom = move_from(m);
941 Square rfrom = move_to(m); // HACK: See comment at beginning of function
944 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
945 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
947 // Find destination squares for king and rook
948 if (rfrom > kfrom) // O-O
950 kto = relative_square(us, SQ_G1);
951 rto = relative_square(us, SQ_F1);
953 kto = relative_square(us, SQ_C1);
954 rto = relative_square(us, SQ_D1);
957 // Remove pieces from source squares:
958 clear_bit(&(byColorBB[us]), kfrom);
959 clear_bit(&(byTypeBB[KING]), kfrom);
960 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
961 clear_bit(&(byColorBB[us]), rfrom);
962 clear_bit(&(byTypeBB[ROOK]), rfrom);
963 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
965 // Put pieces on destination squares:
966 set_bit(&(byColorBB[us]), kto);
967 set_bit(&(byTypeBB[KING]), kto);
968 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
969 set_bit(&(byColorBB[us]), rto);
970 set_bit(&(byTypeBB[ROOK]), rto);
971 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
973 // Update board array
974 Piece king = piece_of_color_and_type(us, KING);
975 Piece rook = piece_of_color_and_type(us, ROOK);
976 board[kfrom] = board[rfrom] = EMPTY;
980 // Update piece lists
981 pieceList[us][KING][index[kfrom]] = kto;
982 pieceList[us][ROOK][index[rfrom]] = rto;
983 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
984 index[kto] = index[kfrom];
987 // Update incremental scores
988 st->value += pst_delta(king, kfrom, kto);
989 st->value += pst_delta(rook, rfrom, rto);
992 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
993 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
995 // Clear en passant square
996 if (st->epSquare != SQ_NONE)
998 st->key ^= zobEp[st->epSquare];
999 st->epSquare = SQ_NONE;
1002 // Update castling rights
1003 st->key ^= zobCastle[st->castleRights];
1004 st->castleRights &= castleRightsMask[kfrom];
1005 st->key ^= zobCastle[st->castleRights];
1007 // Reset rule 50 counter
1010 // Update checkers BB
1011 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1014 sideToMove = opposite_color(sideToMove);
1015 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1021 /// Position::undo_move() unmakes a move. When it returns, the position should
1022 /// be restored to exactly the same state as before the move was made.
1024 void Position::undo_move(Move m) {
1027 assert(move_is_ok(m));
1030 sideToMove = opposite_color(sideToMove);
1032 if (move_is_castle(m))
1034 undo_castle_move(m);
1038 Color us = side_to_move();
1039 Color them = opposite_color(us);
1040 Square from = move_from(m);
1041 Square to = move_to(m);
1042 bool ep = move_is_ep(m);
1043 bool pm = move_is_promotion(m);
1045 PieceType pt = type_of_piece_on(to);
1047 assert(square_is_empty(from));
1048 assert(color_of_piece_on(to) == us);
1049 assert(!pm || relative_rank(us, to) == RANK_8);
1050 assert(!ep || to == st->previous->epSquare);
1051 assert(!ep || relative_rank(us, to) == RANK_6);
1052 assert(!ep || piece_on(to) == piece_of_color_and_type(us, PAWN));
1054 if (pm) // promotion ?
1056 PieceType promotion = move_promotion_piece(m);
1059 assert(promotion >= KNIGHT && promotion <= QUEEN);
1060 assert(piece_on(to) == piece_of_color_and_type(us, promotion));
1062 // Replace promoted piece with a pawn
1063 clear_bit(&(byTypeBB[promotion]), to);
1064 set_bit(&(byTypeBB[PAWN]), to);
1066 // Update piece counts
1067 pieceCount[us][promotion]--;
1068 pieceCount[us][PAWN]++;
1070 // Update piece list replacing promotion piece with a pawn
1071 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1072 index[lastPromotionSquare] = index[to];
1073 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1074 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1075 index[to] = pieceCount[us][PAWN] - 1;
1076 pieceList[us][PAWN][index[to]] = to;
1080 // Put the piece back at the source square
1081 Bitboard move_bb = make_move_bb(to, from);
1082 do_move_bb(&(byColorBB[us]), move_bb);
1083 do_move_bb(&(byTypeBB[pt]), move_bb);
1084 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1086 board[from] = piece_of_color_and_type(us, pt);
1089 // Update piece list
1090 index[from] = index[to];
1091 pieceList[us][pt][index[from]] = from;
1098 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1100 assert(st->capture != KING);
1101 assert(!ep || square_is_empty(capsq));
1103 // Restore the captured piece
1104 set_bit(&(byColorBB[them]), capsq);
1105 set_bit(&(byTypeBB[st->capture]), capsq);
1106 set_bit(&(byTypeBB[0]), capsq);
1108 board[capsq] = piece_of_color_and_type(them, st->capture);
1110 // Update piece count
1111 pieceCount[them][st->capture]++;
1113 // Update piece list, add a new captured piece in capsq square
1114 index[capsq] = pieceCount[them][st->capture] - 1;
1115 pieceList[them][st->capture][index[capsq]] = capsq;
1118 // Finally point our state pointer back to the previous state
1125 /// Position::undo_castle_move() is a private method used to unmake a castling
1126 /// move. It is called from the main Position::undo_move function. Note that
1127 /// castling moves are encoded as "king captures friendly rook" moves, for
1128 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1130 void Position::undo_castle_move(Move m) {
1132 assert(move_is_ok(m));
1133 assert(move_is_castle(m));
1135 // When we have arrived here, some work has already been done by
1136 // Position::undo_move. In particular, the side to move has been switched,
1137 // so the code below is correct.
1138 Color us = side_to_move();
1140 // Find source squares for king and rook
1141 Square kfrom = move_from(m);
1142 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1145 // Find destination squares for king and rook
1146 if (rfrom > kfrom) // O-O
1148 kto = relative_square(us, SQ_G1);
1149 rto = relative_square(us, SQ_F1);
1151 kto = relative_square(us, SQ_C1);
1152 rto = relative_square(us, SQ_D1);
1155 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1156 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1158 // Remove pieces from destination squares:
1159 clear_bit(&(byColorBB[us]), kto);
1160 clear_bit(&(byTypeBB[KING]), kto);
1161 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1162 clear_bit(&(byColorBB[us]), rto);
1163 clear_bit(&(byTypeBB[ROOK]), rto);
1164 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1166 // Put pieces on source squares:
1167 set_bit(&(byColorBB[us]), kfrom);
1168 set_bit(&(byTypeBB[KING]), kfrom);
1169 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1170 set_bit(&(byColorBB[us]), rfrom);
1171 set_bit(&(byTypeBB[ROOK]), rfrom);
1172 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1175 board[rto] = board[kto] = EMPTY;
1176 board[rfrom] = piece_of_color_and_type(us, ROOK);
1177 board[kfrom] = piece_of_color_and_type(us, KING);
1179 // Update piece lists
1180 pieceList[us][KING][index[kto]] = kfrom;
1181 pieceList[us][ROOK][index[rto]] = rfrom;
1182 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1183 index[kfrom] = index[kto];
1186 // Finally point our state pointer back to the previous state
1193 /// Position::do_null_move makes() a "null move": It switches the side to move
1194 /// and updates the hash key without executing any move on the board.
1196 void Position::do_null_move(StateInfo& backupSt) {
1199 assert(!is_check());
1201 // Back up the information necessary to undo the null move to the supplied
1202 // StateInfo object.
1203 // Note that differently from normal case here backupSt is actually used as
1204 // a backup storage not as a new state to be used.
1205 backupSt.key = st->key;
1206 backupSt.epSquare = st->epSquare;
1207 backupSt.value = st->value;
1208 backupSt.previous = st->previous;
1209 backupSt.pliesFromNull = st->pliesFromNull;
1210 st->previous = &backupSt;
1212 // Save the current key to the history[] array, in order to be able to
1213 // detect repetition draws.
1214 history[gamePly] = st->key;
1216 // Update the necessary information
1217 if (st->epSquare != SQ_NONE)
1218 st->key ^= zobEp[st->epSquare];
1220 st->key ^= zobSideToMove;
1221 TT.prefetch(st->key);
1223 sideToMove = opposite_color(sideToMove);
1224 st->epSquare = SQ_NONE;
1226 st->pliesFromNull = 0;
1227 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1232 /// Position::undo_null_move() unmakes a "null move".
1234 void Position::undo_null_move() {
1237 assert(!is_check());
1239 // Restore information from the our backup StateInfo object
1240 StateInfo* backupSt = st->previous;
1241 st->key = backupSt->key;
1242 st->epSquare = backupSt->epSquare;
1243 st->value = backupSt->value;
1244 st->previous = backupSt->previous;
1245 st->pliesFromNull = backupSt->pliesFromNull;
1247 // Update the necessary information
1248 sideToMove = opposite_color(sideToMove);
1254 /// Position::see() is a static exchange evaluator: It tries to estimate the
1255 /// material gain or loss resulting from a move. There are three versions of
1256 /// this function: One which takes a destination square as input, one takes a
1257 /// move, and one which takes a 'from' and a 'to' square. The function does
1258 /// not yet understand promotions captures.
1260 int Position::see(Square to) const {
1262 assert(square_is_ok(to));
1263 return see(SQ_NONE, to);
1266 int Position::see(Move m) const {
1268 assert(move_is_ok(m));
1269 return see(move_from(m), move_to(m));
1272 int Position::see_sign(Move m) const {
1274 assert(move_is_ok(m));
1276 Square from = move_from(m);
1277 Square to = move_to(m);
1279 // Early return if SEE cannot be negative because capturing piece value
1280 // is not bigger then captured one.
1281 if ( midgame_value_of_piece_on(from) <= midgame_value_of_piece_on(to)
1282 && type_of_piece_on(from) != KING)
1285 return see(from, to);
1288 int Position::see(Square from, Square to) const {
1291 static const int seeValues[18] = {
1292 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1293 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1294 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1295 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1299 Bitboard attackers, stmAttackers, b;
1301 assert(square_is_ok(from) || from == SQ_NONE);
1302 assert(square_is_ok(to));
1304 // Initialize colors
1305 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1306 Color them = opposite_color(us);
1308 // Initialize pieces
1309 Piece piece = piece_on(from);
1310 Piece capture = piece_on(to);
1311 Bitboard occ = occupied_squares();
1313 // King cannot be recaptured
1314 if (type_of_piece(piece) == KING)
1315 return seeValues[capture];
1317 // Handle en passant moves
1318 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1320 assert(capture == EMPTY);
1322 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1323 capture = piece_on(capQq);
1324 assert(type_of_piece_on(capQq) == PAWN);
1326 // Remove the captured pawn
1327 clear_bit(&occ, capQq);
1332 // Find all attackers to the destination square, with the moving piece
1333 // removed, but possibly an X-ray attacker added behind it.
1334 clear_bit(&occ, from);
1335 attackers = (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1336 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN))
1337 | (attacks_from<KNIGHT>(to) & pieces(KNIGHT))
1338 | (attacks_from<KING>(to) & pieces(KING))
1339 | (attacks_from<PAWN>(to, WHITE) & pieces(PAWN, BLACK))
1340 | (attacks_from<PAWN>(to, BLACK) & pieces(PAWN, WHITE));
1342 if (from != SQ_NONE)
1345 // If we don't have any attacker we are finished
1346 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1349 // Locate the least valuable attacker to the destination square
1350 // and use it to initialize from square.
1351 stmAttackers = attackers & pieces_of_color(us);
1353 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1356 from = first_1(stmAttackers & pieces(pt));
1357 piece = piece_on(from);
1360 // If the opponent has no attackers we are finished
1361 stmAttackers = attackers & pieces_of_color(them);
1363 return seeValues[capture];
1365 attackers &= occ; // Remove the moving piece
1367 // The destination square is defended, which makes things rather more
1368 // difficult to compute. We proceed by building up a "swap list" containing
1369 // the material gain or loss at each stop in a sequence of captures to the
1370 // destination square, where the sides alternately capture, and always
1371 // capture with the least valuable piece. After each capture, we look for
1372 // new X-ray attacks from behind the capturing piece.
1373 int lastCapturingPieceValue = seeValues[piece];
1374 int swapList[32], n = 1;
1378 swapList[0] = seeValues[capture];
1381 // Locate the least valuable attacker for the side to move. The loop
1382 // below looks like it is potentially infinite, but it isn't. We know
1383 // that the side to move still has at least one attacker left.
1384 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1387 // Remove the attacker we just found from the 'attackers' bitboard,
1388 // and scan for new X-ray attacks behind the attacker.
1389 b = stmAttackers & pieces(pt);
1390 occ ^= (b & (~b + 1));
1391 attackers |= (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1392 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN));
1396 // Add the new entry to the swap list
1398 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1401 // Remember the value of the capturing piece, and change the side to move
1402 // before beginning the next iteration
1403 lastCapturingPieceValue = seeValues[pt];
1404 c = opposite_color(c);
1405 stmAttackers = attackers & pieces_of_color(c);
1407 // Stop after a king capture
1408 if (pt == KING && stmAttackers)
1411 swapList[n++] = QueenValueMidgame*10;
1414 } while (stmAttackers);
1416 // Having built the swap list, we negamax through it to find the best
1417 // achievable score from the point of view of the side to move
1419 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1425 /// Position::saveState() copies the content of the current state
1426 /// inside startState and makes st point to it. This is needed
1427 /// when the st pointee could become stale, as example because
1428 /// the caller is about to going out of scope.
1430 void Position::saveState() {
1434 st->previous = NULL; // as a safe guard
1438 /// Position::clear() erases the position object to a pristine state, with an
1439 /// empty board, white to move, and no castling rights.
1441 void Position::clear() {
1444 memset(st, 0, sizeof(StateInfo));
1445 st->epSquare = SQ_NONE;
1447 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1448 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1449 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1450 memset(index, 0, sizeof(int) * 64);
1452 for (int i = 0; i < 64; i++)
1455 for (int i = 0; i < 8; i++)
1456 for (int j = 0; j < 16; j++)
1457 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1461 initialKFile = FILE_E;
1462 initialKRFile = FILE_H;
1463 initialQRFile = FILE_A;
1467 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1468 /// UCI interface code, whenever a non-reversible move is made in a
1469 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1470 /// for the program to handle games of arbitrary length, as long as the GUI
1471 /// handles draws by the 50 move rule correctly.
1473 void Position::reset_game_ply() {
1479 /// Position::put_piece() puts a piece on the given square of the board,
1480 /// updating the board array, bitboards, and piece counts.
1482 void Position::put_piece(Piece p, Square s) {
1484 Color c = color_of_piece(p);
1485 PieceType pt = type_of_piece(p);
1488 index[s] = pieceCount[c][pt];
1489 pieceList[c][pt][index[s]] = s;
1491 set_bit(&(byTypeBB[pt]), s);
1492 set_bit(&(byColorBB[c]), s);
1493 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1495 pieceCount[c][pt]++;
1499 /// Position::allow_oo() gives the given side the right to castle kingside.
1500 /// Used when setting castling rights during parsing of FEN strings.
1502 void Position::allow_oo(Color c) {
1504 st->castleRights |= (1 + int(c));
1508 /// Position::allow_ooo() gives the given side the right to castle queenside.
1509 /// Used when setting castling rights during parsing of FEN strings.
1511 void Position::allow_ooo(Color c) {
1513 st->castleRights |= (4 + 4*int(c));
1517 /// Position::compute_key() computes the hash key of the position. The hash
1518 /// key is usually updated incrementally as moves are made and unmade, the
1519 /// compute_key() function is only used when a new position is set up, and
1520 /// to verify the correctness of the hash key when running in debug mode.
1522 Key Position::compute_key() const {
1524 Key result = Key(0ULL);
1526 for (Square s = SQ_A1; s <= SQ_H8; s++)
1527 if (square_is_occupied(s))
1528 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1530 if (ep_square() != SQ_NONE)
1531 result ^= zobEp[ep_square()];
1533 result ^= zobCastle[st->castleRights];
1534 if (side_to_move() == BLACK)
1535 result ^= zobSideToMove;
1541 /// Position::compute_pawn_key() computes the hash key of the position. The
1542 /// hash key is usually updated incrementally as moves are made and unmade,
1543 /// the compute_pawn_key() function is only used when a new position is set
1544 /// up, and to verify the correctness of the pawn hash key when running in
1547 Key Position::compute_pawn_key() const {
1549 Key result = Key(0ULL);
1553 for (Color c = WHITE; c <= BLACK; c++)
1555 b = pieces(PAWN, c);
1558 s = pop_1st_bit(&b);
1559 result ^= zobrist[c][PAWN][s];
1566 /// Position::compute_material_key() computes the hash key of the position.
1567 /// The hash key is usually updated incrementally as moves are made and unmade,
1568 /// the compute_material_key() function is only used when a new position is set
1569 /// up, and to verify the correctness of the material hash key when running in
1572 Key Position::compute_material_key() const {
1574 Key result = Key(0ULL);
1575 for (Color c = WHITE; c <= BLACK; c++)
1576 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1578 int count = piece_count(c, pt);
1579 for (int i = 0; i <= count; i++)
1580 result ^= zobMaterial[c][pt][i];
1586 /// Position::compute_value() compute the incremental scores for the middle
1587 /// game and the endgame. These functions are used to initialize the incremental
1588 /// scores when a new position is set up, and to verify that the scores are correctly
1589 /// updated by do_move and undo_move when the program is running in debug mode.
1590 Score Position::compute_value() const {
1592 Score result = make_score(0, 0);
1596 for (Color c = WHITE; c <= BLACK; c++)
1597 for (PieceType pt = PAWN; pt <= KING; pt++)
1602 s = pop_1st_bit(&b);
1603 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1604 result += pst(c, pt, s);
1608 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1613 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1614 /// game material score for the given side. Material scores are updated
1615 /// incrementally during the search, this function is only used while
1616 /// initializing a new Position object.
1618 Value Position::compute_non_pawn_material(Color c) const {
1620 Value result = Value(0);
1622 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1624 Bitboard b = pieces(pt, c);
1627 assert(piece_on(first_1(b)) == piece_of_color_and_type(c, pt));
1629 result += piece_value_midgame(pt);
1636 /// Position::is_draw() tests whether the position is drawn by material,
1637 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1638 /// must be done by the search.
1640 bool Position::is_draw() const {
1642 // Draw by material?
1644 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1647 // Draw by the 50 moves rule?
1648 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1651 // Draw by repetition?
1652 for (int i = 2; i < Min(Min(gamePly, st->rule50), st->pliesFromNull); i += 2)
1653 if (history[gamePly - i] == st->key)
1660 /// Position::is_mate() returns true or false depending on whether the
1661 /// side to move is checkmated.
1663 bool Position::is_mate() const {
1665 MoveStack moves[256];
1666 return is_check() && (generate_moves(*this, moves, false) == moves);
1670 /// Position::has_mate_threat() tests whether a given color has a mate in one
1671 /// from the current position.
1673 bool Position::has_mate_threat(Color c) {
1676 Color stm = side_to_move();
1681 // If the input color is not equal to the side to move, do a null move
1685 MoveStack mlist[120];
1686 bool result = false;
1687 Bitboard pinned = pinned_pieces(sideToMove);
1689 // Generate pseudo-legal non-capture and capture check moves
1690 MoveStack* last = generate_non_capture_checks(*this, mlist);
1691 last = generate_captures(*this, last);
1693 // Loop through the moves, and see if one of them is mate
1694 for (MoveStack* cur = mlist; cur != last; cur++)
1696 Move move = cur->move;
1697 if (!pl_move_is_legal(move, pinned))
1707 // Undo null move, if necessary
1715 /// Position::init_zobrist() is a static member function which initializes the
1716 /// various arrays used to compute hash keys.
1718 void Position::init_zobrist() {
1720 for (int i = 0; i < 2; i++)
1721 for (int j = 0; j < 8; j++)
1722 for (int k = 0; k < 64; k++)
1723 zobrist[i][j][k] = Key(genrand_int64());
1725 for (int i = 0; i < 64; i++)
1726 zobEp[i] = Key(genrand_int64());
1728 for (int i = 0; i < 16; i++)
1729 zobCastle[i] = genrand_int64();
1731 zobSideToMove = genrand_int64();
1733 for (int i = 0; i < 2; i++)
1734 for (int j = 0; j < 8; j++)
1735 for (int k = 0; k < 16; k++)
1736 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
1738 for (int i = 0; i < 16; i++)
1739 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
1741 zobExclusion = genrand_int64();
1745 /// Position::init_piece_square_tables() initializes the piece square tables.
1746 /// This is a two-step operation: First, the white halves of the tables are
1747 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
1748 /// added to each entry if the "Randomness" UCI parameter is non-zero.
1749 /// Second, the black halves of the tables are initialized by mirroring
1750 /// and changing the sign of the corresponding white scores.
1752 void Position::init_piece_square_tables() {
1754 int r = get_option_value_int("Randomness"), i;
1755 for (Square s = SQ_A1; s <= SQ_H8; s++)
1756 for (Piece p = WP; p <= WK; p++)
1758 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
1759 PieceSquareTable[p][s] = make_score(MgPST[p][s] + i, EgPST[p][s] + i);
1762 for (Square s = SQ_A1; s <= SQ_H8; s++)
1763 for (Piece p = BP; p <= BK; p++)
1764 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1768 /// Position::flipped_copy() makes a copy of the input position, but with
1769 /// the white and black sides reversed. This is only useful for debugging,
1770 /// especially for finding evaluation symmetry bugs.
1772 void Position::flipped_copy(const Position& pos) {
1774 assert(pos.is_ok());
1779 for (Square s = SQ_A1; s <= SQ_H8; s++)
1780 if (!pos.square_is_empty(s))
1781 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
1784 sideToMove = opposite_color(pos.side_to_move());
1787 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
1788 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
1789 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
1790 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
1792 initialKFile = pos.initialKFile;
1793 initialKRFile = pos.initialKRFile;
1794 initialQRFile = pos.initialQRFile;
1796 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1797 castleRightsMask[sq] = ALL_CASTLES;
1799 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1800 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1801 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1802 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1803 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1804 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1806 // En passant square
1807 if (pos.st->epSquare != SQ_NONE)
1808 st->epSquare = flip_square(pos.st->epSquare);
1814 st->key = compute_key();
1815 st->pawnKey = compute_pawn_key();
1816 st->materialKey = compute_material_key();
1818 // Incremental scores
1819 st->value = compute_value();
1822 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1823 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1829 /// Position::is_ok() performs some consitency checks for the position object.
1830 /// This is meant to be helpful when debugging.
1832 bool Position::is_ok(int* failedStep) const {
1834 // What features of the position should be verified?
1835 static const bool debugBitboards = false;
1836 static const bool debugKingCount = false;
1837 static const bool debugKingCapture = false;
1838 static const bool debugCheckerCount = false;
1839 static const bool debugKey = false;
1840 static const bool debugMaterialKey = false;
1841 static const bool debugPawnKey = false;
1842 static const bool debugIncrementalEval = false;
1843 static const bool debugNonPawnMaterial = false;
1844 static const bool debugPieceCounts = false;
1845 static const bool debugPieceList = false;
1847 if (failedStep) *failedStep = 1;
1850 if (!color_is_ok(side_to_move()))
1853 // Are the king squares in the position correct?
1854 if (failedStep) (*failedStep)++;
1855 if (piece_on(king_square(WHITE)) != WK)
1858 if (failedStep) (*failedStep)++;
1859 if (piece_on(king_square(BLACK)) != BK)
1863 if (failedStep) (*failedStep)++;
1864 if (!file_is_ok(initialKRFile))
1867 if (!file_is_ok(initialQRFile))
1870 // Do both sides have exactly one king?
1871 if (failedStep) (*failedStep)++;
1874 int kingCount[2] = {0, 0};
1875 for (Square s = SQ_A1; s <= SQ_H8; s++)
1876 if (type_of_piece_on(s) == KING)
1877 kingCount[color_of_piece_on(s)]++;
1879 if (kingCount[0] != 1 || kingCount[1] != 1)
1883 // Can the side to move capture the opponent's king?
1884 if (failedStep) (*failedStep)++;
1885 if (debugKingCapture)
1887 Color us = side_to_move();
1888 Color them = opposite_color(us);
1889 Square ksq = king_square(them);
1890 if (attackers_to(ksq) & pieces_of_color(us))
1894 // Is there more than 2 checkers?
1895 if (failedStep) (*failedStep)++;
1896 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
1900 if (failedStep) (*failedStep)++;
1903 // The intersection of the white and black pieces must be empty
1904 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1907 // The union of the white and black pieces must be equal to all
1909 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1912 // Separate piece type bitboards must have empty intersections
1913 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1914 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1915 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1919 // En passant square OK?
1920 if (failedStep) (*failedStep)++;
1921 if (ep_square() != SQ_NONE)
1923 // The en passant square must be on rank 6, from the point of view of the
1925 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1930 if (failedStep) (*failedStep)++;
1931 if (debugKey && st->key != compute_key())
1934 // Pawn hash key OK?
1935 if (failedStep) (*failedStep)++;
1936 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1939 // Material hash key OK?
1940 if (failedStep) (*failedStep)++;
1941 if (debugMaterialKey && st->materialKey != compute_material_key())
1944 // Incremental eval OK?
1945 if (failedStep) (*failedStep)++;
1946 if (debugIncrementalEval && st->value != compute_value())
1949 // Non-pawn material OK?
1950 if (failedStep) (*failedStep)++;
1951 if (debugNonPawnMaterial)
1953 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
1956 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1961 if (failedStep) (*failedStep)++;
1962 if (debugPieceCounts)
1963 for (Color c = WHITE; c <= BLACK; c++)
1964 for (PieceType pt = PAWN; pt <= KING; pt++)
1965 if (pieceCount[c][pt] != count_1s(pieces(pt, c)))
1968 if (failedStep) (*failedStep)++;
1971 for(Color c = WHITE; c <= BLACK; c++)
1972 for(PieceType pt = PAWN; pt <= KING; pt++)
1973 for(int i = 0; i < pieceCount[c][pt]; i++)
1975 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
1978 if (index[piece_list(c, pt, i)] != i)
1982 if (failedStep) *failedStep = 0;